I. Field of the Invention
This invention relates to rotatable cutting tools, particularly tools having replaceable cutting blades or inserts releasably retained by clamping means in the tool body.
II. Description of Related Art
It is known to provide rotatable tools comprising a tool body and one or more replaceable blades or inserts for machining operations. An insert for these tools comprises a cutting element made of a relatively long wearing material chosen for compatibility with the material to be cut and comprising one or more cutting edges. An insert may further comprise a holder for mounting the cuffing element to the tool body. A tool body for such tools comprises at least one recess for receiving a replaceable insert and the tool further comprises means for releasably retaining the inserts on the tool body. Tools of this type include drilling tools, boring tools, reaming tools and milling tools.
A particular type of rotatable tool is a tool for machining valve seats in cylinder heads of internal combustion engines, the tool having cutting inserts arrayed on the periphery of the tool and having a reaming tool for machining the valve stem guide bore. As the number of valves per cylinder have increased and overall engine dimensions have decreased, valve diameters have decreased. Consequently tools for performing valve seat machining operations are required to retain cutting blades or inserts in tool bodies having reduced diameters. Known tools for such applications, such as disclosed in U.S. Pat. No. 5,704,741, have included exchangeable cartridges for retaining replaceable cutting inserts. With the demand for smaller diameter valves, smaller diameter tools are required, reducing the tool body volume that can be consumed with blade retaining devices.
FIGS. 1a and 1b illustrate one known tool wherein the replaceable blades are retained in recesses in the tool body by clamping screws. In FIG. 1a, replaceable blades 112 and 114 are retained in recesses of tool body 110. As shown with respect to replaceable blade 112, clamping screws 116 are transverse to recess 118 (FIG. 1b) and are threadably engaged with tool body 110. With replaceable blade 112 in place in recess 118, advance of clamping screws 116 into tool body 110 clamps blade 112 (shown dashed in FIG. 1b) against a side wall of recess 118. As shown in FIG. 1a, plural screws are used and are spaced apart to distribute the clamping forces over the length of the blade to improve resistance of the blade to displacement from cutting forces and from distortion from clamping forces.
FIGS. 1c and 1d illustrate an alternative known clamping arrangement for retaining replaceable tools in a tool body. In FIG. 1c, replaceable blades 122 and 124 are retained in recesses of tool body 120. As shown with respect to replaceable blade 122, wedges 128 are held in recesses 130 adjacent blade receiving recess 132 (FIG. 1d) by screws 126. Screws 126 are threadably engaged with tool body 120. With replaceable blade 122 in place in recess 132, advance of screws 126 into tool body 120 advances the forward edges of wedges 128 to clamp blade 122 (shown dashed in FIG. 1d) against a sidewall of recess 132. Each of wedges 128 serves to distribute the forces from each of screws 126 over larger portions of blade 122 than would be done by the screws alone as in the arrangement of FIG. 1a. However, while larger wedges would provide improved distribution of forces, large wedge receiving recesses, such as recesses 130 are not desirable because of the attendant weakening of the tool body.
In light of the shortcomings of the known clamping means as illustrated in FIGS. 1a and 1c, there remains a need for improved clamping means for replaceable blades in rotating tools.